1. Field of the Invention
The present invention is directed in general to digital radio broadcast transmitters and receivers and methods for operating them. In one aspect, the present invention relates to a system for transmitting digital signal information to digital radio broadcast receivers with increased throughput.
2. Description of the Related Art
Digital radio broadcasting technology delivers digital audio and data services to mobile, portable, and fixed receivers using existing radio bands. One type of digital radio broadcasting, referred to as in-band on-channel (IBOC) digital radio broadcasting, transmits digital radio and analog radio broadcast signals simultaneously on the same frequency using digitally modulated subcarriers or sidebands to multiplex digital information on an AM or FM analog modulated carrier signal. HD Radio™ technology, developed by iBiquify Digital Corporation, is one example of an IBOC implementation for digital radio broadcasting and reception. With IBOC digital radio broadcasting, signals can be transmitted in a hybrid format including an analog modulated carrier in combination with a plurality of digitally modulated carriers or in an all-digital format wherein the analog modulated carrier is not used. In the hybrid mode, broadcasters may continue to transmit analog AM and FM simultaneously with higher-quality and more robust digital signals, allowing themselves and their listeners to convert from analog-to-digital radio while maintaining their current frequency allocations. Another feature of IBOC digital radio broadcasting is the digital transmission capability to simultaneously transmit both digitized audio and data so that one or more digital audio programs can be broadcast within a single logical channel, alone or in combination with data messages, such as metadata (e.g., the artist, song title, or station call letters), special messages (e.g., event, news, traffic, and weather information), or other message information that can all be scrolled across a radio receiver's display while the user listens to a radio station. While the increasing amount of digitized information (e.g., audio, data, audio and data messages) being transmitted requires increased system capabilities, the throughput of existing IBOC digital radio systems may not be sufficient for providing the increasing number of services. For example, there have been solutions proposed for increasing the system throughput while maintaining backwards compatibility to retaining existing services, but the best case expected increase in throughput was approximately 112 kbps. Such an increase in system throughput using the existing IBOC digital radio signal can be realized by creating a multi-level (‘local cloud’) modulation around the original constellation points of the existing IBOC digital radio signal, but such solutions may have required power increase by approximately 11 dB for bringing the new throughput performance to the already established level of performance for existing receivers. Another challenge for HD Radio system transmitter and receiver configurations using two digital sidebands for carrying the exact same payload over each sideband using complementary error correction mechanisms is the perception that, in order to maintain backwards compatibility and avoid obsoleting existing receivers, it is not possible to simultaneously use two digital sidebands in a configuration such that the payload and the error correction mechanism on one sideband (either one or both) are different from the payload and error correction mechanism on the other sideband. Because of at least the demonstrated challenges for increasing system throughput without noticeably reducing system performance (e.g., coverage), the existing solutions for delivering digital audio and data services with increasing number of services and features are extremely difficult at a practical level.